Thermodynamic machine

A method of operating a thermodynamic machine as an engine and/or as a heat pump of a Stirling cycle type, the method comprising the steps of:

• a) providing a thermodynamic machine operable as a heat engine and a heat pump, the thermodynamic machine comprising:
• an expansion cylinder defining an expansion chamber, a compression cylinder defining a compression chamber and respective pistons reciprocally movable in the chambers during operation of the machine;
• a regenerator disposed between and in communication with the expansion and compression chambers, wherein the regenerator comprises a regenerator chamber and wherein the thermodynamic machine is arranged such that substantially the whole volume of a working fluid will pass through said regenerator chamber twice during a single cycle of the thermodynamic machine;
• a first heat exchanger in communication with the expansion chamber and the said regenerator chamber and a second heat exchanger in communication with the compression chamber and the said regenerator chamber;
• a first bypass conduit connecting the expansion chamber with the said regenerator chamber bypassing the first heat exchanger and a second bypass conduit connecting the compression chamber with the said regenerator chamber bypassing the second heat exchanger;
• wherein the only heat supplied to or removed from the volume of working fluid is that supplied or removed by the said first and said second heat exchangers;
• wherein the machine comprises at least a pair of valves;
• one valve being provided between the expansion chamber and the first heat exchanger or between the first heat exchanger and the said regenerator chamber or in the first bypass conduit between the expansion chamber and the said regenerator chamber;
• and the other valve being provided between the compression chamber and the second heat exchanger or between the second heat exchanger and the said regenerator chamber or in the second bypass conduit between the compression chamber and the said regenerator chamber;
• and
• b) timing at least one of the valves such that flow of working fluid is controlled through the or each valve over time at least once during each cycle of the thermodynamic machine, so as to direct working fluid of the machine between the said regenerator chamber and the expansion and compression chambers either substantially through the respective bypass conduit or substantially through the respective heat exchanger at pre-determined stages of the machine cycle;
• whereby the working fluid is isolated from the said heat exchangers when it is necessary to bypass the said heat exchangers, and the working fluid is prevented from bypassing the said heat exchangers when it is necessary for the working fluid to pass through the said heat exchangers.